Seveneves: A Novel by Stephenson Neal

Author:Stephenson, Neal [Stephenson, Neal]
Language: eng
Format: azw3, epub, mobi
Publisher: HarperCollins
Published: 2015-05-18T16:00:00+00:00

THE SCRAPE WITH THE ATMOSPHERE HAD LEFT YMIR TUMBLING slowly as it hurtled away from the Earth on its new orbit. Calculating exactly what that orbit was took them fifteen or twenty minutes, and told them that they had fewer than four hours in which to take actions needed to save their lives.

If all had gone perfectly, the nuclear burn would have slowed Ymir down to the point where a rendezvous with Izzy could then have been achieved with a few small additional delta vees. They had hoped this might happen, but not seriously expected it. The best they could really hope for was to shed some velocity and reduce the height of their apogee.

That figure—the distance separating the Earth and the ship at the top of her orbit—was directly related to how much velocity she had at the bottom. Because Ymir had “fallen” in from an extremely high apogee, far beyond the moon’s former orbit, she had come in screaming hot for her skip off the atmosphere. Every bit of velocity that was killed by the huge nuclear retro-rocket burn, or by friction with the air, translated into a lower altitude at the succeeding apogee, which—depending on how the numbers had worked out—would occur weeks, days, or hours later.

The answer, once they had run the numbers, turned out to be hours.

In one sense, Ymir had missed her target by a mile; the total delta vee she had achieved had been less than a third of what they’d hoped for. And yet this had been enough to bring her apogee down from far beyond the moon’s orbit to a figure only about thrice the altitude at which Izzy circled the Earth.

Likewise, the period—the amount of time it took to complete an orbit—had dropped from seventy-five days to a mere eight hours. The lesson being that huge alterations in those figures could be purchased for comparatively small amounts of delta vee.

Bringing Ymir the rest of the way down to Izzy’s orbit, on the other hand, would require twice as much delta vee as they’d wrung out of the “burn” just completed.

Long before worrying about that, however, they would have to survive the next eight hours.

Ymir’s apogee might have been radically altered, but her perigee altitude was unchanged—meaning that it was still dangerously low. If they took no action, the next go-round would therefore bring them roaring and bouncing across the top of the atmosphere again.

On one level, raising the perigee a bit, so that they’d never have to worry about the atmosphere again, was an easy task. They could do it with a small but precisely calibrated burn at apogee. In a normal space mission, such a thing would have been straightforward. Here, it was complicated by two factors. First of all, their success in lowering the apogee, and shortening the period, had imposed a tight deadline—four hours after perigee—when that burn needed to occur.

The second complication was the ship’s slow tumble. This meant that their nuclear rocket engine was never pointed in the right direction, save by lucky accident.

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